Humidity

 Environmental Factors

August 18th, 2022

    Weather and aviation go hand in hand and therefore being a pilot also means being a part time meteorologist. Every pilot wants a clear sunny day to fly in but that's not always the case. Every time you fly, you will have to take into account the weather. You can see the obvious like rain, low clouds and wind but one thing you cannot see but may be able to feel is humidity. Humidity simply means the amount of water vapor is in the air. 

    I learned how to fly in Florida on the gulf cost (KCGC) and you can guarantee that it was always going to be 90 percent or more humid everyday. Humidity is not necessarily a factor while at cruising altitude but it is during takeoff. Engine performance output is calculated on cool, dry days and it doesn't take into account the water content. The water vapor that is drawn into the engine is non-combustable and therefore you will need to enrich your fuel/air ratio to combat it. The resulting horsepower loss can cause a longer rollout on takeoff and a poor climbing rate as well. When the air temperature dips down a bit and the humidity is high you may also run into the carburetor icing conditions. The icing conditions can start when its 50-70 degrees with a relative humidity above 60 percent. The engine will let you know if you have carb ice building up. It will start to run rough and if not taking care of, can result in an engine failing. It can happen at any altitude if the conditions are present, even in Florida where it is sunny year around.

references 

Water Content of the Atmosphere

https://www.flight-mechanic.com/water-content-of-the-atmosphere/

Carburetor Icing 

https://www.aopa.org/-/media/Files/AOPA/Home/Pilot%20Resources/ASI/Safety%20Briefs/SB09.pdf

Photo

Williams, James, September 2020 over the Florida everglades.